Not all of the heated wearables are industrialized at the production line, but they are industrialized during the PCBA design phase.
The majority of the wearable projects are not thought to fail because a prototype project on the first attempt failed. When the product enters into volume production, they stall, unprofitability or produce too much field returns. The underlying reason is nearly identical: prerogative PCBA design choices were made without giving careful thought to the manner in which the board would perform in actual manufacturing variability, test coverage specs, component supply variations and operator handling at volume.
Numerous OEMs and brands continue to work on the basis that the manufacturing issues can still be designed out once the design is frozen by either using more fixtures, more operators, stricter process controls, or by making changes to the layout at the last hour. As a matter of fact, the window of meaningful industrialization has closed way before SMT lines begin to yield. Most of your future yield, throughput, cost as well as reliability risks will already be determined by the time you reach pilot builds.
The trend is longstanding it has been observed over the last ten years since managing dozens of NPI transitions involving heated apparel products it is that the most scale-ups go well in efforts to consider manufacturability, testability, and production stability as non-negotiable design inputs since schematic capture.
Why Heated Wearables Are Difficult to Scale in Mass Production
Because they are challenging to industrialize at mass, the category of consumer electronics Heated wearables is among the hardest to industrialize challenges.
The underlying challenge is that, in an inherently rigid electronics (PCBA), flexibly-spun-textiles (heating components, wiring harnesses) and high-energy-density-battery product, in a system required to endure repeated mechanical loading, temperature variation and even human sweat, must be tightly coupled, to both electrical and thermal margins. This level of cross-domain complexity is hardly witnessed in normal consumer electronics.
Variation in component, shrinkage of the textile, consistency of battery cells, consistency of connector mating, handling by operator all are forms of variability which scale exponentially. A five per cent change in resistance of a heating element, and a three per cent reduction in voltage drop across a marginal battery cell, could drive an otherwise marginal PCBA design into intermittent failure land, the failures which do not show up on engineering models made by competent technicians.
How PCBA Design Decisions Affect Manufacturability
It is common to identify every significant headache in manufactured wearables to be linked to a specific choice of PCBAs.
The most conspicuous one is component selection. Single-source risk due to use of parts with long lead times, or second-source equivalents that are unstable ensures supply discontinuity and pushes requalifications that are unsightly and expensive. Even decisions in layout can have an impact: lack of access to test-points, close fiducials, small pad separation leading to solder bridging at high-speed lines, vias near component bodies, and poor thermal relief on high-current pads are all practices that have a direct negative impact on first-pass yield.
Test-point planning is often disregarded. Functional test coverage is reduced without strategically located, strong test points which support bed-of-nails fixtures and automated optical inspection (AOI), so manual or slower, costly tests have to be used.
To help teams considerate of mitigating these pitfalls at an early phase in their development, the most effective risk-reduction activity is to build PCBA design for scalable heated wearable manufacturing into the core development process is the single most effective risk-reduction step.
Prototype Success vs Production Reality
There is virtually no difference between prototypes and volume production units- and the difference is rarely due to sloppy assembly.
Engineering samples are normally hand-soldered or assembled on small lines with cherry-picked components, ideal reflow profiles and no mechanical stress on connectors. The reality of production is much different: parts which are assembled into batches with broader tolerances, reflow ovens are constantly running and there is thermal drift, connectors are further assembled and tested nearly a dozen times, and boards are flexed in response to integrating textiles.
A PCBA that is almost specification on golden samples frequently gives targets with the variations of components, solder joint reliability, and connector contact resistance no longer in the ideal. Minimum-margin designs, be it electrical design, thermal design, or mechanical design, just do not make it to live conditions in actual production.
Testing Strategy as a Bottleneck in Heated Wearable Production
The greatest throughput killer is often testing in scaling the wearable which is heated.
The infrastructure testing should ensure the functionality of the inline heating performance, temperature control, battery protection, and communication (including or excluding), and the safety interlocks, in seconds per unit. When the PCBA does not have adequate coverage of its tests or even accessible nodes, the production can only be based on slow hand testing or incomplete testing and the daily production is limited.
Manual testing is not cost-effective at speeds of less than several thousand units per month. Each increment of seconds per board during the functional test has the immediate impact of lowering line capacity. Unsuitable test-point design or diagnostic-mode absence will cause an extension of debug time, as compared to the situation in which the failures happen, and cause a bottleneck that may propagate all down the line.
The generic collection of design shortcomings that common PCBA design mistakes that prevent heated apparel from scaling.
Battery Integration Challenges During Mass Production
Actually, Battery integration grows exponentially with volumes of production.
Even different cells of the same batch can vary, leading to different charging characteristics, incongruency in protection circuit triggering, and runtime complaints. Pack-to-PCBA interfaces assemblies of connectors, flex cables, solder pads = These high-risk locations of intermittent contact become hazardous when the connection is required to undergo many cycles of insertion/removal during assembly and subsequent use by the end user.
Battery procedure manuals also become very constrained in size. ESD sensitivity, moisture exposure during assembly, and accidental short during textile integration becomes a practical concern which was insignificant in a prototype stage. Designs lacking sound battery defense and user interface redundancy cost much in rework and in-the-field returns.
To understand this very important field more, consult battery protection circuit design, see battery protection circuit design for mass-produced heated clothing.
Firmware Stability and Version Control at Production Scale
One of the most pernicious reasons of the post-launch failures of the heated wearables is firmware drift.
Even relatively small modifications to pilot to volume firmware; e.g. bug fix, calibration, optimization, etc., may introduce non-obvious regressions that will not be noticed until thousands of units are deployed. In the absence of rigid version locking, build tracking, and change discipline, it is virtually impossible to tell whether an issue in a field is due to a change in hardware or to a change in firmware.
The PCBA and firmware should be handled as a system that is very close. Any software update program should be checked against the complete spectrum of variation of production components and assembly tolerance and not only golden samples.
How OEMs Should Plan PCBA Industrialization From Day One
To achieve successful industrialization, the change of thinking between design-centric and production-centric needs to be conducted at the beginning of the project.
Key practices include:
- Conducting DFM (Design for Manufacturability) reviews at schematic stage, and not after layout.
- Engaging production engineers and test development that occurs when selecting components and reviewing the layout.
- Risk assessment (FMEA) during supply chain, assembly, testing and textile integration.
- Incorporating production-intent test coverage through the PCBA of the initial revision.
- Ensuring formal change control and version discipline of hardware as well as firmware.
Teams which regard industrialization as an upward activity and not a downstream undertaking have significantly fewer shocks when launching pilot and ramp-up.
In-house PCBA design and production validation capability describes parterning companies in-house PCBA design and production validation capability.
Conclusion — Industrialization Is a Design Discipline
Mass productions of heated wearables through additional capacity cannot succeed but PCBA designs that look ahead towards variability, test, and production reality.
Industrialization is not another stage after the completion of the design, it is a complex of planned engineering decisions during the development process. Once the PCBA layout, component choice, test strategy, battery interface, and firmware discipline has matched the reality of very-large-scale manufacturing, scale-up can be predictable and profitable as opposed to the chaos and cost of huge scale-up. The factory is not the one that makes the product reliable in a heated apparel, it is the design.